With the Montague, CS 2012 XC Races just a few weeks away, I thought it would be a good time to introduce the latest version of the Ascendant XC.

I flew the Ascendant XC-II FEAR for most of last summer and got a feel for its strengths and where improvement could be made. Then I sat down at the computer and pulled together all of my notes and feedback from others who had flown the sailplane and made some design changes.

The fuselage design was modified from a three-piece fuselage with a slide-on nose cone to a pod and canopy version. This change seemed more practical for use in the field and reduced the time and materials needed to produce a fuselage pod.

The next change was the wing. The airfoils used in the original wings were the XC designed Dr. Drela airfoils in the AG2X series. While these proved viable on a flapless and aileronless wing (as called for on the XCBD), they did not suit me as well as I liked. Since the JW00-JW03 airfoils were not available I went back to the AG4X series of airfoils. This also changed the shape of the wing and I pushed the wing length to 189" to get to 4.8M wingspan. The black colored wing bottoms were kept as well as the bright white tops for visibility reasons.

Right about the time I was redesigning the wing, Anker through hiis research into making stronger and lighter wings had come up with a new spar technique. This seems like as good a place to test the new spar design. The new center panel is no longer a stressed-skin design and now has a major CF spar system. The result was a stronger wing that was lighter. However, it was a little more involved to built and the cost of the wing went up a bit. The tips are flat with no dihedral and now sport full length ailerons. because of the large length of these tips, the ailerons were split into and inner and an outer aileron. I plane to play with some crow settings later on with these ailerons. The overall dihedral flavor of the wing changes as well. since we went with full span ailerons combined with flaps, I changed the dihedral between the center panel and the tip panels to 5-degrees -- down from 8-degrees. This left the center panel dihedral at 4.5-degrees. To simplify the design, I changed the center panel dihedral to also be 5-degrees. During the development we went with a 0.625" ID CF tune in the spar system (up from 0.5" ID on the previous wings). This meant new wing joiners had to be made. I made a set of molds that built 8" long joiners (4" per side) at 5-degrees. These joiners come in 2 flavors: solid and hollow. The solid joiners are 53 grams and the hollow joiners are 33 grams. This saved over a pound out of the wing by going with CF joiners over steel joiners. Now back to the center panel dihedral being changed to 5-degrees . . . We use 1 of the solid joiners here in the center panel to strengthen where the spar system comes together. The single mold can make all three joiners.

This time around I made my own CF boom. I learned that boom making is not easy and mistakes add up in terms of cost and time. The current Ascendant AC will use a boom but the next one will use a fuselage built from a mold. But i have to build that mold yet so that is a topic for another thread.

The boom will support the vertical fin and rudder hanging off of the back and a V-mount will support a fully-flying stabilizer for pitch control.

Below are two CAD renditions of the fuselage and the entire sailplane. even though the fuselage rendition shows that this is the "V" model, I have moved beyond that and this is actually the AXC-VI (the 6th in the series). as for the wing, I guess we can call it the FEAAR wing ;-P

This year the electronics onboard will decouple the RX and telemetry systems from the batteries that power the servos. This eliminates pulling a lot of current through a very small receiver and will keep the voltage clean to the RX and Telemetry systems. There will be 2 GPS units onboard, one powered by the RX/Telemetry battery and the other is self powered with its ow internal battery. there will be a common Ground line between the batteries in the RX and Servo systems so that there is no "signal level" issues at the servos from a floating ground level.

So where are the pictures? I have a lot of pictures that I have taken over the past several weeks of building and fabrication and I'll get selected ones posted soon. The sailplane is ready to be assembled tonight. The wings are complete and already attached to the fuselage. I have to mount the fin/rudder to the boom, mount the V-mount, mount the boom to the fuselage and add in the rudder and elevator servos and the remaining electronics. Yes I also have to balance the plane. If all goes well, I will be hand-tossing this version on Friday and possibly some winch launches before the end of the holiday weekend.

The molds this time around were designed with using the inflatable-bladder method and each mold half is keyed to the other half. With the new design of the fuselage, I only needed two molds instead of the six from last year's fuselage design (which is still available). The new aft fuselage design will be capable of supporting both of my fuselage designs as well as the XCBD fuselage. I may remake the XCBD fuselage molds so that they too can use the inflatable bladder method. However, due to time constraints to get this plane ready for Montague, the fuselage I have now was vacuum bagged under 29" of Hg.

Tonight I'll find out how much lead, if any, I need to add to the nose to achieve a proper balance. After that I can report on the total all up weight RTF for the plane. Anker and I have already noted several areas in the wings and fuselage where we can save additional weight (up to 18 ounces -- a non-trivial amount of weight). I am confident that this version of the AXC will again be under the FAI 5Kg limit. we both took a little longer this time so that we could ensure that the molds and processes in the manufacture of the AXC were ready to produce copies of the design to interested parties.

Take Care,
John
---------------------------------------------------------------------------
Each day Begins with a whole new set of possibilities
---------------------------------------------------------------------------

Some promised pictures of the new Ascendant XC. We made the first hand-tosses today. Now the plane is back in the shop for a minor tweak and will be ready for its first winch launches tomorrow.

Currently the sailplane is under the 5Kg weight restriction. The next time I build this plane I can shave off even more weight ... so I can add the weight back as ballast.

After tomorrow's flights, I have to start constructing the shipping crate and get this sailplane packed up and on its way to Montague, CA.

Take Care,
John
---------------------------------------------------------------------
Each day Begins with a whole new set of possibilities
---------------------------------------------------------------------

Today we got a chance to launch the new Ascendant XC off of my winch on a medium length launch line. All in all, today's flights were fantastic.

The sailplane signals lift well, climbs easily, and lands at almost hand-catch speed. Usually I'm playing with the elevator to flap mixing forever, but today we hit it on the first try. We adjusted the launch mode just a little and are getting great launches off of the winch. We put 10 flights on the sailplane today, most were short 5 minute flights but others were longer in the 10-15 minute range. I could hear lots of cameras clicking away but was focused on flying the plane and my camera sat idle. So I have no pictures to post today but an hoping that some will show up in my inbox so that I can share them here.

I'm also breaking in a new radio. Normally I pull the factory springs out and replace them with really stiff springs. I like it that way so I know when I'm accidentally feeding in up elevator when working the ailerons. But most people don't like that and last year is was a discussion point when we were passing my TX around while competing on the course. Another issue is that I usually fly with 60-70% expo enabled. This definitely takes some getting used to if you don't fly regularly with expo. So this year, no expo, just straight stick.

Next up: Build a shipping crate. Maybe I'll take the night off before I start operating rotating cutting tools like a table saw . . .

Take Care,
John
---------------------------------------------------------------------
Each day Begins with a whole new set of possibilities
---------------------------------------------------------------------

Here are those photos, John. You did a great job with this plane. It flew so well. You've got to be proud after all your hard work. Steady as you could want in the air and indicates lift really well. I'm sure you'll do well in Montague.

A huge glider like this introduces some expected and some unexpected challenges.

In the former category is cutting cores this large, handling 70" by 40" pieces of cloth, barely being able to fit the panels into my heat box, and finding room to trial fit the tips to the center panel.

In the latter category is having to help air migrate out from between the Mylars and the core. This has never been a problem with smaller wings, but with wings this size you have to push the air out by stroking the completed, and partially evacuated, bag from the center towards the edges. If you don't do this you get extremely unsightly bubbles in the finished wing skin.

Building a 190" span wing at 11 lbs is surprisingly hard. Weight goes up by the cube of the scale, so large planes tend to have higher wing loadings than small ones. At the maximum FAI allowed wing area and maximum weight the wing loading is just under 11 oz/sq ft, very low for a ship this size.

A huge glider like this introduces some expected and some unexpected challenges.

In the former category is cutting cores this large, handling 70" by 40" pieces of cloth, barely being able to fit the panels into my heat box, and finding room to trial fit the tips to the center panel.

In the latter category is having to help air migrate out from between the Mylars and the core. This has never been a problem with smaller wings, but with wings this size you have to push the air out by stroking the completed, and partially evacuated, bag from the center towards the edges. If you don't do this you get extremely unsightly bubbles in the finished wing skin.

Building a 190" span wing at 11 lbs is surprisingly hard. Weight goes up by the cube of the scale, so large planes tend to have higher wing loadings than small ones. At the maximum FAI allowed wing area and maximum weight the wing loading is just under 11 oz/sq ft, very low for a ship this size.

Anker

Anker/John,

Do you have numbers for the wing area and root chord? I think the FAI max area of 2325 sq inches includes the stab area.

Do you have numbers for the wing area and root chord? I think the FAI max area of 2325 sq inches includes the stab area.

Steve

The wing area is 2167.0745 square inches and the Stab area is 150 square inches. Together they equal 2317.0745 square inches. That leaves a 7.9255 square inch margin below the FAI limit.

The root chord is 14". The entire sailplane ready to fly is under the 5Kg FAI weight limit.

Take Care,
John
---------------------------------------------------------------------
Each day Begins with a whole new set of possibilities
---------------------------------------------------------------------

The Ascendant XC was shipped off today in a custom built plywood box to CA today. Can't wait to get out there and get some more stick time on the AXC.

Take Care,
John
---------------------------------------------------------------------
Each day Begins with a whole new set of possibilities
---------------------------------------------------------------------

Well it has certainly been an interesting summer working on the Ascendant XC. But now it is getting cold outside and my focus is turning in to my shop and thinking about next year’s trials. I know I haven’t put much into this thread lately, so let me update you to what’s been going on.

After I got back from CA I was less than pleased with the performance of the AXC even accounting for the weather conditions out there this year. I continued to trim out the AXC and took it to the NATS for some more field tests and although it performed better, it still was not where I was expecting the performance to be. In fact, this version of the AXC was performing below its predecessor. So armed with a couple of data recorders, two telemetry systems, and two variometers, I set out to baseline the performance of this version of the AXC. The rules I used for these performance benchmarks were rather strict and took a long time to get the baseline nailed down and be repeatable.

Basically I would watch the NOAA weather reports for my area and would go out to my local field before dawn on days with 0-mph predictions. I would set up the launch gear in the dark with a headlamp and await the sunrise. As soon as it was light enough to see the plane throughout its planned flight I would start the testing. The basic test was to launch, establish a dead-glide over my field of duration 30-60 seconds then I would pull up and do a modified stall turn to generate a mark in the recorded logs then I would do a 180-degree turn and come back across the field with another pull up at the end followed by a second pull up to get two marks in the logs. Later on I would use the logs to determine the sink rate of the AXC by averaging these two passes. If either variometer chirped upward movement during the tests (either pass) the test run was invalidated and scraped. I’d keep repeating these tests with slightly different elevator trim settings controlling the speed of the AXC. In New England, 0-mph mornings happen about every 8-9 days. The initial tests were done in “cruise mode” and the results were a 160 ft/min sink rate at 23.4 mph. I executed the tests again in “thermal mode” and came up with 152 ft/min sink rate. A quick check with some long time XC fliers indicated that the SBXC and the MXC would fly at ~90 ft/min sink rate at 21 mph.

So back into the shop I went to figure out whether it is a design flaw or a fabrication error or pilot error causing the poor min sink results. I decided to attack drag on the sailplane first. I went over every inch of the sailplane and made a series of changes at one time mostly because the weather was not cooperating with good test opportunities. The first change was to fair in the exposed control rod tubes on the outside of the fuselage boom. I removed the external switch jacks and made them internal. The wing was bagged with the correct airfoils if the wing were to have a full-length set of moving trailing edges. However, my wing design called for several sections of the TE to be fixed. These fixed sections helped with setting the degree of deflection for the flaps and all 4 ailerons. Unfortunately these sections accounted for 10% of the TE and were permanently stuck in reflex mode. This to me seemed like a high ROI change. So I cut the fixed sections free from the wing and attached them to the closest movable surface (flap or aileron). The wing center section could not be changed without modifying the wing saddle area so I left this section alone. I think I was getting 80% efficiency out of the TE of the wing and now was 97.8% efficiency at the TE. In doing this I felt I needed to add a 2nd anti-rotation pin to each of the wing tip panels and ensured the tip panels were properly aligned to the center panel. Next I went over the leading edge and made up several laser-cut LE templates and ensured that the LE conformed to the templates and that they were sealed with thin CA and hard. The last change I made was to take double-sided sticky tape and thin drafting Mylar cut into 1” wide strips and went around the wing and sealed off the open part of the V left when making the hinges for the ailerons and flaps. I did the same for the rudder. The Mylar is taped to the wing side ahead of the gap and the Mylar extends aft of the V. I rebalanced the model on the input that some people who had flown the AXC felt it was a tad nose-heavy and removed 24 grams of nose weight. With all of the extra gear (telemetry and varios and batteries) the plane’s weight was 11 lbs. 10 ounces (without the extra equipment the weight is under the 5Kg FAI weight limit).

Armed with these changes the weather cooperated to give me 2.5 hours of dead air so I was out again before dawn to repeat the tests. The first flight was a line break and I used what altitude I had to get the plane trimmed for level flight and then started the tests. Between each flight/test I would move the elevator by 4 clicks of the trim. I have no idea exactly how much this changed the elevator position but I felt it was a good starting point. After I had all of the tests and the varios were beginning to chirp more than not I called it a day for testing. After reviewing the data collected I had some surprising results. I do not have the exact measurements with me as I write this, but these numbers will be close. I found that my second flight of the day was the best where I recorded 3 minutes of flight a 60 ft/min sink rate at 24.2 mph. later on at 19 mph I recorded 90 ft/min sink rate. I did have one test run at 24.6 mph which had a min sink rate of 90 ft/min. So there appeared to be a significant increase in sink rate between 24.2 and 24.6 mph. Equally interesting was the return to the 90 ft/min sink rate as the speed slowed from 24.2 to 18-19 mph. I don’t have a way of locking in the speed of the sailplane to measure the sink rate at a specific speed. But this was close enough to tell me that I don’t want to be flying faster than 24 mph if I want min sink rate flying and too slow is just as bad.

This was all well and good but the proof was in flying under actual flight conditions. Out I went onto a 10K G&R course. The wind was 10-15 mph cross wind (about 40-degrees to the course). None of the planes flying that day made it above 2100 ft AGL. The AXC made it 13 km before setting down alongside the road my mistake was to turn back looking for lift behind me instead of pushing forward (pilot error). Afterwards we (the 10K team) were thinking about the flights and we put the AXC up for some test flights and trimming flights. Now the AXC is using Dr. Drela’s AG4X series airfoils and I was told that they do not require aileron differential. So initially, I had 100:100 differential set but had moved it to 100:50 (Up : Down) at the NATS but now we had an opportunity to fly into the wind and observe the AXC at close range. We could clearly see that the nose would significantly skid to the right when a left aileron roll was initiated. Subsequent flights reduced the down aileron deflection which reduced the right skid for left aileron control until we had no right skid. This corresponded to 100:0 aileron differential. It is also important to note that with aileron control was mixed 30% rudder movement. We also increased the percentage of rudder movement to the aileron input until we had a clean roll left and right. At this point my experimentation ended since the weather had continued to deteriorate and we felt it was time to get everything broken down and stored. I did add another flight mode to be used during landing so that when the flaps are deployed the aileron differential goes back to 100:50 to increase control close to the ground (and I was used to landing with that aileron differential setting).

Now that winter is approaching and the flying season is ending I’ll be working in the shop on improvements to the design. For starters, I’m almost ready to cast a new fuselage mold to address the center section of the wing’s TE being at reflex instead of cruise. This was not the only reason for a new mold but it did give me the opportunity to work this fix into the new plug. I’ll also be working on improving my skills in making booms for the AXC. The existing boom is 0.070” thick and 260 grams. It has been rock-solid but I believe that it is over-kill for the AXC’s needs. Yes I want something strong enough to handle an off-field landing but I think I can do that at 80-100 grams. Which will provide a weight savings from the tail of 60-80 grams and 120-160 grams from the nose (balance weight) – 6 to 8 ounces lighter is good. I can always add the weight back in to the plane in the form of ballast centered on the CG rather than at the extremities of the fuselage.

One last point to make is the balance point on the wing. Before all of the tinkering that I did to the fuselage and wings people who flew the plane felt it might be a tad nose-heavy. I had done a 45-degree dive test and felt that the plane was shallowing out of the dive – which is good for an XC ship. But just the same I removed 24g from the nose and made all of the test flights and real-world flights. After we adjusted the aileron differential one of the comments was that it looked like the plane was tail heavy. So again while the plane was airborne we put it into a 45-degree dive and let go of the sticks. The AXC tucked its nose under and headed for the ground. A quick yank on the elevator saved the ship but impressed all of us how fast a plane can lose altitude when pointing at the ground. I put the 24 g back into the nose. Now it is important to state that the initial dive tests were done at 18-19 mph and the new test was done at 24 mph. The speed of the plane does have an effect on the CG of the airplane and the additional speed may have played a part in the test. Then again there were some corrections added behind the CG. It is important to note that regardless of what the airplane calculators say about where your optimal CG should be located that the plane itself is the ultimate authority based on your style of flying. I’ll take a little more directional stability over a twitchy plane that has to be constantly corrected in flight, that is to say I like it a little more nose-heavy than not.

That’s it for now. By the spring time I should have new fuselages and new booms ready for sale (if anyone is interested in them) and the wings will also be available. I’m toying with the idea of a built-up wing as well. The issue right now with a built-up wing is the tips get very thin and it is hard to work the tips and maintain the airfoil’s accuracy. I have all winter to solve that problem

Take Care,
John
---------------------------------------------------------------------------
Each day Begins with a whole new set of possibilities
---------------------------------------------------------------------------

Thanks for publishing this data. A lot of hard work went into this and it payed off. The lessons about drag are particularly interesting. I can offer a few tips I learned from Joe Wurts, Mark Drela, and Philip Kolb before you get too deep into the redesign.

The first thing I would do is take the time to model the task. Think about what you want the plane to do and then how to represent it. Think about how you would plug a given design into the model and come up with a means to compare at the end.

To then model the plane I would recommend becoming proficient with XFLR5. There is a bit of a learning curve but the info is out there if you dig deep enough. Scale a given design up and down 10%, plug it into the course model, and see what happens. I was often surprised by the results. As Joe told me, once I learned how to model the course the optimized design stood out.

Finally I would study every last page of the Supra plans. All the information is relevant to bigger planes, and the attention to detail is fantastic.

Good luck. We are all watching with interest what you are doing and hoping to see you next year out on course.